1. Field of the Invention
The invention relates to a high-resolution, preferably adjustment-free tiltsensor and a method for determining the tilt angle of the tiltsensor.
2. Description of the Related Art
The use of high-resolution tiltsensors is known in the fields of geodesy, geophysics and geotechnics. A resolution of one microradiant or better is required in order to measure tiniest movements of objects. This high resolution is achieved by specially designed methods and sophisticated circuitry, but also by accepting a small measuring range of the tilt angle. The latter usually lies at approximately ±1. These tiltsensors have a curved spirit level that contains an electrically conducting (electrolytic) liquid as well as a small gas bubble. The position of the gas bubble varies according to the tilt of the spirit level and is scanned by three electrodes. Such a high-resolution constructive design is shown in the User's Manual Series 755, 756 and 757 Miniature Tilt Sensors, Applied Geomechanics Inc., Santa Cruz, Calif. 95062 USA.
Due to the small measuring range available at high resolution, plumb (vertical) adjustment is necessary. Only then it is possible to take advantage of the small measuring range. The effort involved in adjustment for the installation of a single tiltsensor, which is typically meant to provide measurement results for a period of months or even years, is relatively minor. Adjustment expenses become significant at the latest when, in the course of long-term measurements, it becomes apparent that the measuring range will be exceeded and that a readjustment of the tiltsensor will become necessary. Readjustment generally makes measurements difficult and costly. The effort put into adjustment is also particularly relevant in conjunction with the installation of a large number of tiltsensors, for example when a large surface area must be covered by several tiltsensors to measure deformations in the earth's surface. Finally, applications are presently available which allow little or no adjustment, for example in the installations of tiltsensors in extreme environments, such as at the edge of volcanoes or along the sea bed.
In order to achieve high angular resolution and precision, an angle calibration is made on the tiltsensor. This means that the electric output signals supplied by the electrodes are assigned to the correct angular quantities on the basis of standardized comparison measurements.
The object of the invention is to develop a tiltsensor which has a tilt angle measuring range that is significantly greater than about ±5° or even greater than about ±10° and at the same time exhibits a significantly better angular resolution than 1 microradiant. In addition, the sensor should be simple to manufacture, yet be less susceptible to malfunctioning, have a high lifetime stability and be economical to service. A tiltsensor described in the User's Manual Series 755, 756 and 757 Miniature Tilt Sensors, Applied Geomechanics Inc., Santa Cruz, Calif. 95062 USA features these characteristics, but fails to provide the desired, enlarged tilt angle measuring range.